A digital communication network comprises devices linked together by a communication bus, for example the IEEE 1394 bus, using wires or waves. The communication network comprises, for example, the following devices: a terminal allowing users to display audiovisual emissions, to enter parameters for controlling the network and to ascertain the state of the network, a digital television receiver (a decoder for example) capable of receiving audiovisual emissions and service information originating from a transmission network, a device for storing the audiovisual emissions, a modem, etc. The list of devices is not exhaustive, likewise there may be several of some devices within the communication network, for example a camera in each child's room.
The 1394 network enables devices to communicate according to three different modes: the synchronous mode where the data packets are emitted regularly at the end of determined time periods, the asynchronous mode where each message is isolated from the others and can be emitted at any moment, the isochronous mode where the data packets are emitted regularly in a determined time bracket. These various communication modes are used for the transfer of specific data. Commands are generally transmitted in asynchronous mode, data transmitted in synchronous mode, and stream data internal to the network in isochronous mode. In the latter case, we find monitoring data emitted by a camera disposed in a child's room, a television displaying said data. In contradistinction to the audiovisual data received from a transmission network and subjected to very precise and regular synchronizations, such a monitoring need only receive an image from time to time, at moments which can vary.
The monitoring of proper networked device operation is generally performed by a device inherent in the device. We find for example “Watchdog” devices, which triggers an error message when at the end of a timer, the central unit being monitored has not performed a certain action. This device must quite obviously be more reliable than the central unit that it is charged with monitoring. Each device being monitored must possess its own device, the present invention makes it possible among other advantage, to limit the number of monitoring devices while being able to monitor a significant number of devices.
The document U.S. Pat. No. 6,430,629 B1—SMYERS, published on 6 Aug. 2002 describes a 1394 network, and the possibility of monitoring the temperature of rooms by virtue of modules communicating with the aid of this network. The invention relates more precisely to the “monitoring” of the state of a device of a network. A screen indicates the device state such as a VCR or an STB, and the temperature of the room. Claim 1 indicates that the network monitor periodically receives information indicating the state of the devices.
The document EP 1 185 034—SONY teaches error detection in a network, for example 1394, emission loop. A device of the network is configured to detect connection errors on an isochronous channel, the error detection is performed inter alia by polling of the signals “IEEE 1394 signal S1”. Other detections can be performed by analyzing the regularity of emission of the data packets thereby defining a priority level in the error and a specific action, for example the display on a screen of the error detection. This document teaches a device exercising monitoring on all the communications of the network and not specifically on a device desiring to be monitored.